The participation of xanthate and dithiocarbamate compounds in free radical reactions has been previously reported. The participation of dithiocarbamate and xanthate salts in free radical reactions appears very complex and occasionally contradictory. In rubbers which include unsaturated sites (e.g. natural rubber, polybutadienes and various unsaturated copolymers), these compounds are frequently used as vulcanizing agents, usually in conjunction with at least one other compounds. Examples are the abstracts of JP (1982)/102974 and EP 184301. Similar activity is reported for saturated rubbers containing small amounts of epoxy or halo groups (U.S. Pat. Nos. 3,525,721 and 4,524,185). Fe or Mg dialkyldithiocarbamates cause cure of mercaptan terminated polymers in the presence of air (U.S. Pat. No. 3,991,039).
Use of xanthate or dithiocarbamate salts is taught as part of a peroxy catalyst system for emulsion polymerization of chloroprene monomer and comonomer mixtures in U.S. Pat. No. 4,814,401.
In U.S. Pat. No. 3,639,370 dialkyldithiocarbamates with an unsaturated peroxy compound such as t-butyl permalinate or t-butyl perethyl fumerate are taught as a low temperature polymerization initiation system for vinyl compounds such as acrylic esters and unsaturated polyesters.
On the other hand, dithiocarbamates are also reported as free radical inhibitors in other polymerization or vulcanization reactions.
In U.S. Pat. Nos. 3,378,510 and 4,632,950 dialkyldithiocarbamate salts are disclosed as scorch retarders (on i.e. inhibitors of premature vulcanization) for peroxy vulcanized saturated rubbery polymers. (U.S. Pat. No. 4,632,950 also identifies chlorinated polyethylene, 1,4-polybutadiene and fluoroelastomers as suitable polymers.)
U.S. Pat. No. 4,018,604 teaches dialkyldithiolcarbamates (e.g. Zn dimethlydithiolcarbamate) as an additive to prevent fogging of non-silver free radical photosensitive films.
U.S. Pat. No. 4,021,310 teaches use of O.sub.2, copper dialkyldithiolcarbamates and a conventional inhibitor such hydroquinone as inhibitors of polymerization in fractional distillations of acrylic monomers. Table 1 of this reference demonstrates that the dithiocarbamate is an essential ingredient of this inhibitor system.
JP (1986)/76578 describes a two-liquid type resin composition utilizing an acrylic monomer. A peroxide (e.g. cumene hydroperoxide) is placed in one part of the composition and a vanadium compound, together with a nickel xanthate compound are used in the second part. At least a portion of the monomer must have an additional functional group, as for instance a carboxylic or phosphate acid group, a hydroxy, amino amide or ether group. This reference discloses that the xanthate compound acts as a stabilizer against decomposition of the vanadium compound, and as an inhibitor against premature gelling of the vanadium containing monomer solution, not as an active ingredient of the cure system.
Xanthate and dithiocarbamate compounds have also been reported in photoinitiated or photo crosslinked polymer systems but only in systems which included a conventional radical photoinitiator (an organic aryl carbonyl photoinitiator) or in which the xanthate or dithiocarbamate specie were terminal ester groups on a prepolymer. References showing use of a dithiocarbamate metal salt in a photocurable composition free of an aryl carbonyl photoinitiator are not known.
Macromolecules, 21 2297-9 (1988) appears to disclose a xanthate ligand polymer for initiating polymerization of a quartanary ammonium complex salt of styrene sulfonic acid.
Poly. Prep. Am. Chem. Soc. Div. Polym. Chem., 29, 6-7 (1988) describes photoinitiated polymerization of styrene and methylmethacrylate. The initiator is a tetraethylthiuram disulfide which thermally initiates the formation of a polymer having terminal dithiocarbamate ester or ligand groups. These groups in turn can be photolyzed to initiate polymerization of a second monomer. The dithiocarbamates are not metal salts. JP (1989)/29401 reportedly contains a similar disclosure.
JP (1986)/77046 is reported as describing photocuring compositions for printing plates including acrylic monomers, a conventional film forming polymer, a photoinitiator and a metal dithiocarbamate salt such as nickel di-n-butyldithiolcarbamate. A chlorinated triazine compound is included in the example formulation.
JP (1974)/6203 is reported to describe a heat developable photographic material employing a dithiocarbamate (e.g. Na diethyldithiocarbamate) and an aromatic carbonyl compound (e.g. 9,10-phenanthraquinone) as photosensitizers for PVC resins coated on polyester films. No image was formed when the 9,10-phenanthraquinone was omitted from the composition.